Area Monitoring of Namco Lake in Summer by High-resolution TerraSAR-X Spotlight Mode

Namco lake is the second largest lake on the Tibetan Plateau as well as the highest large lake in the world, which is located in the south central Tibetan Plateau, with a total area of 2020.66 km(2) and a total catchment area of 10,680 km(2). The usefulness of traditional optical images highly depends on cloudless weather conditions and suitable solar illumination, while lake area detection procedures in optical images might be prevented by the presence of shadows, variations in solar illumination, and geometric distortions. In contrast, SAR imagery has its advantage of relative insensitivity to atmospheric conditions and independence from sun illumination. In this work, high-resolution TerraSAR-X spotlight mode images are utilized to monitor area fluctuation in Namco. As narrow observation area is the expense of high resolution in SAR imaging, scene size of TerraSAR-X high-resolution spotlight mode is only 5km * 10km (Azimuth* Range). Therefore, for a great lake around 2000 km(2) such as Namco, the selection of observation position is very important for assessing the resolution accuracy. Based on the lake bathymetric survey data, the northeast corner of Namco is chosen as the observation area, as the most obvious water level fluctuations is located in this part. To quantitative calculation the water area of lake from temporal SAR images, A four-step approach is proposed: 1) Orthorectification and Data Coregistration; 2) Speckle Filtering; 3) Segmentation of SAR Image; 4) Water Area Detection and Calculation. The quantitative analysis of the water area, which is calculated utilizing the corresponding technique mentioned above, are 32982205, and 33253869 m(2) in July 11, 2014 and August 2, 2014, respectively. The largest area change part is located in the valley region, with lake area increasing by 79824 m(2). In accordance with prior investigation and meteorological data set, the average precipitation, glacial meltwater supply, as well as runoff reaches the maximum of the whole year in the duration from June to September on Tibet Plateau. Thus it is easy to understand the extensive tendency of the lake.